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In this forum,I have seen ice dams referred to, but I haven’t seen an explanation of how they form. I fear the answer is going to be painfully simple and therefore I have disguised my name to avoid embarassement.
Does the “moist” in hot moist air have anything to do with the ice or is it simply carried along with the “hot”?
Replies
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I'm no expert, but....The snow on the roof melts, the water runs down the roof. But the edges of the roof are colder than the rest of the roof, because there is no living area below them. The water freezes at that point. When enough water has frozen along the edge, there is no place for more water to go, and it starts backing up, literally flowing uphill under the shingles and hence a leak. When you see posts about a cold roof design, that is to prevent the snow from melting in the first place.
Rich
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I never had one before last night. We had about six hours of sleet here in South East PA and then the temp rose after midnight and it has been pouring ever since. I have a shed dormer on my third floor and it started leaking through a nail hole in the old cedar shake roof. Luckily my 14 month old woke up at 3:00 am otherwise I wouldn't have caught it until this morning. It is the strangest weather I have ever seen.
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Alan, I've never heard of using a 14-month-old as an early warning system. Ingenious! (My apologies to the tyke.)
Seriously, we've been pelted by snow & freezing rain in No. VA ... and yesterday when I looked across at the new house next door I exclaimed "Freddy was right!" All the snow melt was over the rafter bays, and each rafter was clearly outlined with snow. Never would have noticed this before. So, in weather that was still below freezing, snowmelt was running down the roof to refreeze on the colder eaves, risking ... an icedam.
Now, this is terrible. Fiberglas is a better insulator than wood, but the rafters let much less heat reach the roof than the fiberglas! I assume this was either due to (1) really bad convection within the fiberglas and/or (2) outright warm air leaks through the ceiling and out the ridge vent (convection again). Most of the houses in the neighborhood look like this. Of course, our nearly uninsulated 60-y.o. house was another story -- no ice on our roof...
If I had a new house and this sort of problem, I would be rather annoyed.
*Eerie, Freddy: I wrote my comment at the same time you wrote your dissertation on roof ice, and now it appears to refer to your post I hadn't read.In high school chem, I think the heat of fusion was 80 cal/gram and vaporization was 540 cal/gram -- while heating a gram of water 1 degree Celsius takes just 1 calorie. So Freddy's figures are, as usual, quite scientific. I'm not try to show off, rather I think it's interesting that I can remember figures from 15 years ago but can't remember where I left my checkbook.
*I suspect the rafters are "highlighted" on the roof because they are in direct contact with the (cold) roof, and are therefore quite chilled (approaching the temperature of the outdoors). Since it will take longer (and more thermal energy) to heat a 2x8 or 2x10 cold solid object (the rafter) than the adjacent air in the attic, I would expect those rafter lines to persist until they reach an above-freezing temperature (either through heat transfer from warmer surrounding attic air or as roof is heated by sunlight).
*All of that is very clear, Fred. I only have 2 questions. What is snow? Why do people keep it on their roof? It seem to me that if there is a danger of it melting, that it would be better to put it in the freezer. I was thinking about this this morning, when I took the dog out. It was cold so I put on sandals and a t-shirt, rather than going out in my shorts. For the sake of research I looked at all the houses in my neighborhood, and I can safely say that no one in San Diego keeps snow on the roof. Is this some kind of regionalism?
*Hey Fred,You wouldn't want to lend your enlightenment to the discussion of the behavior of gases over on the "Pressure Plans" thread, would ya? I'm looking for a concise discription of the dynamics of the Stack Effect and the ever-abused notion of the neutral pressure plane.Steve
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Fine, Mike. Rub it in to the rest of us who are freezing our little toboggan's off. By the way, do you have pontoons in your basement for when the whole coast slides halfway to Hawaii?
Just kidding :-) gotta go split some more firewood...
Shivveringly, Lisa
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After the BIG ONE everything EAST of the San Andreas fault will fall into the Atlantic Ocean.
*Seems that Fred pretty well fills the bill on ice dams. Lets not over look the easy answers that stump some of us sometimes. Like snow filling a gutter and backing up leaving water to back fill the soffit to drip down the wall (Took a few days to figure that one out)
*As a reformed Californian, I have learned the pleasure of having actual seasons. A life with seasons now appeals more than suspended animation in ... San Diego.I also quite like how things here can spin out of control at any moment, like a Texas driver in icing conditions. As opposed to the unfathomable weirdness across the river from me in D.C.
*Fred:I had a very large chicken burrito with extra hot sauce, washed down with a couple nice cold Leinenkugels, perfectly chilled in the snow outside my backdoor. Tommorrow I may have some enlightenment over at the "interior pressure thread"Loving the whitestuff as I watch the ice accumulate on the eaves. Oh well, just another project awaits...fixing the last owners fg mishaps.Yours in HV and HF, Dave
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Mike
In keeping with your very astute observations, but not yet having read them, I climbed up on my roof and spent the day moving about 3' of fluffy white stuff ( before it became heavy white stuff) over the edge and into my yard where the guy who delivers my furnace oil had to climb through a 5' drift and fell into a basement window well and damn near broke his leg, while my dog, thinking he was acting very strangely tried to rip his arm off, while I looked on from on high.
It's definitely a regional thing.
Snowbound in southern Ontario
Patrick
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Hey, Fred. I share your facination over the physical properties of water. Tell me, what liquid, other than water, will expand in volume with an increase or decrease in temperature?
*These Ice Dams Can be Serious. But I can't. Fifteen thousand years ago, during the last Ice Age, an ice dam collapsed in what is now northern Idaho, releasing the waters of a giant inland sea known as Lake Missoula. Five hundred cubic miles of water rampaged westward at 60 miles an hour in a torrent flowing with ten times the volume of all the rivers on earth. The flood carved canyons, gouged out enormous plunge pools, made rivers like the Snake and the Willamette run backward and scoured the earth of eastern Washington right down to bare basalt rock.
*Yahooooo! Way to go Fred! You are right about the alcohols you named. There is another material which expands with an increase or decrease with temperature. Hint: it is a metal.I too, am simply fascinated by "hydrogen bonding", as you call it.On another note: what do you suppose the latent energy of a miniscus to be? To keep it simple, let's suppose the fluid is DI water.Particularly yours, Rich
*Dave, Perfectly chilled burritos must be a regional favorite where you live.
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I thought a minicus was about half a microswear. they are measured in arghs, I believe.
Happy days. :-)
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No, no, Fred, nobody looks dumb here. You seemed as if you may know. If you don't want to 'play', fine. Actually, these are questions I have carried around for some time now.
I'm not enough of the mathematician/engineer to figure out the miniscus thing. (Hey, was I the only one to study irrelevant problems in college? Anyway, on the T question, mercury is a possible answer. Thank you for your irreplaceable time.
Curiously, Rich
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Check out the Certified Contractors Network for info on Ice Dams.
Check Out : http://www.contractors.net
Rich D.
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Rich. I checked out the contractor's net on ice dams.One or two put emphasis on sealing, but there could have been a stronger emphasis on sealing the basement ceiling and the attic floor, as the first line of defense against ice dam formation.GeneL.
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To learn more about Ice Dams and a list of Internet links to information resources see
http://www.contractors.net/fr_dams.html
Richard Kaller, Certified Contractors NetWork
To learn more about the NetWork see
http://www.contractors.net
*I am not sure what Fred was trying to say, but, to my absolute horror, I came away with the impression that he believed less ventilation was better.As is so often the case, the problem, like the solution, is simple!All of my experience has taught me that it is essential for the venting to be through the attic in an upward direction, from the eaves to the peak.You have a serious problem which I believe will only corrected with added ventilation near the peak (which may or may not require the addition of ventilation past those blocks) you mentioned and eave ventilation.If you have a cool attic, you won't have snow melting on your roof. If you don't ventilate, warm air is trapped in the attic, gathers near the top, warms the under side of the roof, snow melts, runs down til it hits the cooler eaves, freezes, backs up and, causes major problems. This is not rocket science. Gable end vents or roof vents provide good sources of ventilation; roof vents continue to work under snow cover, breathing - just as a person can survive being buried under an avalanche for some time. My personal preference would be to gable end vents (assuming you have gable ends and an attic in conjuction with your cathedral ceiling) because they are less likely to be covered by snow and will breathe better.I realize that I live in Alberta where the air is usually very dry and the temp. can vary from -40 to +90 (once in a while, if we are lucky), but the priciples are the same, ventilate, ventilate, ventilate. My ventilation (for a 1350 sq.ft. bungalow with a simple gable roof) consists of two large gable end vents and one turbine vent in the middleof the roof towards the top. I can guarantee you that if I go up to the attic today, the temperaturewill be within 5 degrees of the outside air temp. andthere will be no frost (to melt and wet my insulation) and there will be no water running down on top of my roof to form an ice dam.There are plenty of older houses in this area with poor sealing of house leaks and/or poor insulation. The reason they have lasted is stricktly good ventilation.
*Well Fred, it looks like the only thing we have in commoncommon is our feelings about turbine roof vents. They have been often shown to be no more effective than standard roof vents. Unfortunately, it was there when I bought the house.Right or wrong, the building code mandates the installtion of attic venting, whether through the use roof vents or gable vents or whatever,but it must be in addition to the soffit venting. Perhaps you would like the job of rewriting the buildingcode???? I can recommend a few other changes that you could incorporate when you take on that task.Maintaining the attic temperature at or near the ambient outside temperature, contrary to what you might say, is a success. It is an indication (and only an indication) that the air in the attic is being exchanged with the outside air, that any warm moist air that escapesfrom the interior of the house is being carried away and not being allowed to condense on the cold attic surfaces.As to my building so poorly as to need attic ventilation, the house was not built by me, but by some other so-called "reputable" builder about 45 years ago. Yes, perhaps some builders can build well enough so as to not need attic ventilation. Unfortunately, most of them do not build as well as they think (or say)they can and houses still need attic ventilation.I quit building some years ago. The crap that some of the other cotractors were putting together(and some still are) was embarrassing and I was apalled at what people were buying (and still are buying).As to your comment about the cost of my heat, it was under $700.00 last year. What was yours? I have been slowly retrofitting the house since I bought it in 1991, and the cost of gas is still six dollars a month less than when I bought it.Why do I want to get rid of the heat that has escaped from my 45 year old house? So it does'nt melt the snow on the roof and cause ice damming; so the moisture in that air does not get a chance to condense on the cold framing members etc. andwet the insulation when it warms up.Now maybe if you have some way of taking care of the leaks that some careless builder left in my house and if you have some way of stopping the snow from melting on the roof (due to that escaping heat) I will follow your advice and close up my roof and gable vents. Until that time, the vents stay where they are. On the other hand, the turbine you can have any time you hear of someone foolish enough to want one; I'll trade it tomorrow!!!! (Well make that in a couple of months, after the three feet of snow that is on my roof has melted - hopefully melted due to the arrival of spring and not poor ventilation.)
*
TEST
*Simon. This is an appropriate time to qote a fellow Canadian--i'm american-- Y.E. forgues: "Ganble vents have a series of blased sloped at 45 degrees. If not properly designed, they may allow rain or snow to enter the roof space....In regions such as the Prairies,which are subject to fine,windf-driven snow, gable vents may have to be closed in winter to prevernt snow from accumulating in attics." And American Vietnam veterans tell of the sand in barrack attics blown in through gable-end vents. And a very recent post on Breaktime tells of an attic full of snow brought in through gable-end vents. By the bye. Does the 1995 edition of the Canadian Building Code have an alternative methods and materials section? GeneL
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Joe;
I understand what you are saying and I tend to
agree.
Fred:
I understand what you are trying to say too.
unfortunately there are still some things that
need to be pointed out:
1. It is extremely difficult (if not impossible)
to get a perfect seal between the interior and
the attic. Without a perfect seal, you had better
have some means of getting rid of any humidity that
escapes to the attic.
2. The R factor of insulation is only a measure
of its resistance to heat transfer, and does not
indicate a complete barrier to heat transfer. (even R70
allows heat some heat transfer) Given that, if
the heat which passes through the insulation is
allowed to gather in the attic and warms the
underside of the roof, snow melt will occur
with possible ice damming (depending upon the amount
of heat escape).
3. Given that it is extremely difficult to seal
perfectly a newly constructed building, it is even
more so with an existing house with about 16 inches
of loose insulation in the attic (or with a cathedral
ceiling. Failing that ability, one should be prepared
to get rid of the humidity that is gathering in the
attic, not condoning blocking the vents.
Out of interest, I consulted the Alberta Building Code
1997 edition and found the I erred (partly) in the
venting requirements. The requirement is 1/300 for
slopes greater than 1/6; 1/150 for lesser slopes.
Only 25% of the venting is required to be at or near
the top of the attic space.
Of interest, the appendix (which of course is
non-regulatory and only explanatory) recognizes
some buildings (specific types) may have
sufficiently tight seals to permit the non-use of
ventilation, but, site built housing is not part
of that select group and venting is still
required.
Gene L:
Gable end vents certainly may allow the infiltration
of snow, but normally they are: under an overhang
where there is less chance of snow blowing in; often
built with deep enough slats that combined with the
baffling effect, not much snow actually gets in
(and personally, I have never heard this to be a
problem,although there is, I am sure,many problems
I have not heard of), and; any gable end vent
that I have seen, is constructed with a screen
material incorporated into them (to help prevent
insects from setting up home in your nice dry,
ventillated attic) which would also severly
limit the amount of snow getting in. Our snow
here probably is usually coarser than the
sand/dust which you describe.
There is a small section in the NBC which recognizes
alternatives to both materials and test methods, but I
suspect you have about as much chance of getting by that
one as humidity does of getting out of an unvented attic!
Cheers
*
Interesting article in the JLC that arrived today about some major builders building whole developments without vents and code officials going along with it. This specific article was addressing "hot climates" (ave. monthly temps exceed 45 f and annual rainfall greater than 20") but the same builder is doing the same north of Chicago.
*Fred You'll be pleased to know that the Ontario building code now allows attic spaces that are packed with insul (no air space above- as in Cathedral type) to be unvented. Also, I think it was Gene L. who announced some months back, that the Canadian Housing Corp. (CMHC) is doing testing into one of your favourite theories on dense pack cells being impermeable to vapor transfer in attic spaces. Anything like this happening stateside?Never a flag waver-Patrick
*Hey FredYou've got me a little confused, again. "Moisture does diffuse readily through cells and we depend on that"? I thought one of the aspects of dp cells that got you most excited was it's supposed impermiability to moisture transfer hence its supposed ideal application as a retrofit in walls and attics without previously installed vapour barriers/retarders. Haven't you also stated that dp cells tend to hold that moisture that was mixed into them as part of the 'blowing in process' which you felt was good for keeping the framing from completely drying out over time???Merci bien for the tip on Jacques Rousseau.No jingoism here. . . -Pat
*Patrick - Whats "that moisture that was mixed into them as part of the 'blowing in process' "? The ones I blow are bone dry. Gary said something about wet cells also. Are we discussing completely different systems and processes?
*BillIt's been my understanding for quite some time now, after reading numerous posts from Fred and others, that the 'dp cells' were blown in with a moist binder, as part of the 'dense pack' procedure; the other type of install. known as loose fill cells. I'll look through a series of posts that I printed for myself from threads earlier in the summer that make reference to this.
*Dense pack doesn't require moisture to the best of my knowledge - at least not the way Fred taught me. Its blowing dry cells very lean - lots of air and little cells - and they pack tightly rather than fluffy. Same machine - just the gate on the material hopper. Try it - you might like it. And you really don't need a sub - its easy to do.
*Patrick. Some are confusing blown-in with sprayed-in or incorrectly mixing or exchanging the terms.GeneL.
*Patrick and Bill. Dense Pack is dry blown-in.See the post(Bill you quoted Fred as saying that no VDR was necessary with cellulose because it was a VDR. I responded by saying I did not know perm rating of cellulose and continued on with Harold Orr's 1985 report). His report was about the 4 Canadian built in 1900 and insulated in 1925 with cellulose and no vapor barriers (sic).Harold explains about the absorbing and rejection of moisture in cellulose. I was just looking for my copy of that report..no luck. At least my cluttered desk prevents me from having a sick mind.GeneL
*I am sure you have covered this somewhere before, but I am sure you have covered ALL of this several times, so I will ask for one more time. From the inside of the wall there is: gypsum board; wood studs with cels in the bays; wood sheathing. Followed by housewrap? felt? And the wood sheathing is ??Just trying to get a handle....Thanks.Rich Beckman
*
Fred, I'm very interested in your recommendations for a house I'm designing in Park City, UT (snow!). First, how would you handle the cathedral ceilings? Typically, here they use 12" TJIs and FG batts. I want to use DP cells, but here is the kicker. I talked to our local inspector, and he said that venting is required. If I use FG batts, an airspace is not required between the FG and roof sheathing. Supposedly, a FG manufacturer has provided him data to show that venting will still occur in the upper layer of FG, so the airspace isn't required. However, if I use DP cells, the airspace is required. He said he doesn't know of any exemption for DP cells. This is supposedly national not local code. Does this sound right to you? I thought of using 14" TJIs. In order to handle the DP cells and still keep an airspace, I thought of wedging rigid foam board between the TJI webs up against the flanges. Then after all except the upper sheet of drywall is installed, blow in dry cellulose. A local insulation sub said that they use scrap cardboard instead of the rigid foam. This doesn't sound very sound to me. It also seems you recommend not using a vapor barrier. Is that correct? Next, what about the walls? I don't think that I want to deviate from the standard 2X6 done here. However, the insulation sub said that they haven't done dry DP cells with netting for years, and the preferred method is wet blown in. He said the only binder is water and equated it to a spitwad. Is this the same application that is referred to as DP cells with a binder? It is shaved flush to the studs, and drywall hung after it dries. Trying to learn, Dave
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Bill, to avoid drilling holes in the "Ply-Bead" I planned to use on our porch, I cut a piece of scrap 1/4" plexiglas the size of the stud bay and put a 2' hole through it. This way I could fill the uncovered bays and watch too! It was interesting to see how the space filled, including the swirl marks left by the spinning of the air current. Quite a chore to hold the plexiglas hard enough against the wall to keep gray fluff from squirting out too!
Speaking of gray fluff, the mess we made in the driveway made me sentimental for those Boston winters I remember so well...
*Gene - If I said that it was a mistake - because I clearly don't believe cellulose is a vdr. What I did say is that it will seel against air infiltration.Please, I have enough trouble without having something I didn't say ascribed to me. Please tell me where I said this and I will correct it.I would count on cellulose allowing moisture to diffuse through it.
*
Well Fred, as citizen subject to Canadian building codes I do give an "ice dam" about them. No other questions being asked or answers requested where, indeed, does your cold weather construction expertise come from.
Charles
*Your plexiglass technique sounds like a very interesting idea. I was thinking of doing the same thing with plywood/OSB, and using sheetrock screws to temporarily hold it in place. How well did it work for you? Do the DP cells hold firm once the plexigass is removed? How long prior to installing sheetrock? This sounds like it would solve the problem of getting the insul inspected, and you wouldn't have to drill holes through the sheetrock or install it in stages leaving the top open.
*Fred: Thank you for your suggestions. Regarding the cathedral ceilings, is venting required by national code? I see above references to Canadian code, but not US. How do you get this approved in new construction where you are? You mentioned trying the "it settles" ploy, but how would that pass an inspection? Assuming I'm unable to convince the local inspector, and I have to use a vent chute, how would you suggest I do it? I gather you don't think my idea of using rigid foam to form a chute is a good idea since it would act as a vapor "retarder" and keep moisture within the insulation. Is that correct? How about using a wood product instead? Stapling in 1/8" material seems like it would work. I know this doesn't follow your "anti-venting" philosophy, but again I'm talking about the best way to vent assuming I'm required to. You also seem against the water binded cells in the walls. How then do you suggest installing the DP cells? Drill holes in the sheetrock after it's installed, or with 9' ceilings, install 8' of sheetrock and wait on the upper 1' until after DP cells? A post above talked about temporarily covering the bay (in his case with plexiglass). This sounds like an interesting idea, especially if the DP cells hold their form. It would solve any inspection problems. What do you think?Still learning,Dave L.
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I just cored some holes in scraps of 1X6 - since the sheathing and attic floor were 1X6 - and held it against the studs. Once I figured it out, I'd use rages to better seal. No need to use screws. Removed, the cells held firm and flat - no bulge - kind of amazing the first time.
*Gentlemen. Have any of you ever heard of the "Story Jig" named after the inventor Ed Story? It is a clear plexiglass panel that contains 4 gasketed holes. The panel is placed over the wall studs and the cellulose is blown through the openings. It has a locking bar that holds it in place. Fill one stud bay, remove the jig and go onto the next bay. the cellulose--blown to 3.5pcf remains in place. I first learned of this product in 1990. GeneL.
*
As convection is movement of air and diffusion is movement of molecules without air currents, where do you see movement of air currents in a wall?
*
Fred. Under the mistaken,if I read you correctly,belief the we will soon have a national building code, I have been asking when something is to be done about a national, uniform building inspector.This code then, will be everywhere the same, but building inspectors everywhere are not the same. No I don't want unthinking robots...this is what the code says and you must comply. What is the point of a national building code if we have 10,000 different ointerpretations of the same section? Frustrated GeneL.
*"slipped a double into your adult beverage"???? What the *** is a "double" that fits into a drink?Just wondering,Rich Beckman
*We are all operating under the assumption that the US will indeed have a single model building code supported by all three model building code organizations, correct? And I think the OTFD code under this umbrella organization is already in print.Of course it remains to be seen how many jurisdictions will adopt the model code as their code.And none of this changes the sometimes inconsistent interpretation ........ which is actually quite a bit better for the building codes than for ADAAG.
*I lost track of this thread through all the changes to the board!The packing worked great, as Bill said. I cut the plastic so it would fit all of the variously spaced stud bays. Actually, a couple of the knee walls haven't been enclosed yet (a week or two) and the cellulose is standing firm (been busy). Interestingly, I can't for the life of me pack in additional cellulose by hand -- it won't stay. The blow-in definitely packs the stuff tight. The plexiglas was also nice for a beginner (me) because I could confirm what was happening and that I'd done it right. But plywood/OSB would be fine and wouldn't bow out in the center -- maybe with a couple of reinforcing strips -- as the plastic did a little. But hey, as they said in "Body Double," I like to watchI'd propose a compromise -- install the bottom half of the drywall, then blow in cels with a half-bay cover, finish up. For me the less dinking around with taping, the better.Bill -- what are "rages"? I'd like to use the same method downstairs. Happy to use screws...
*Sorry Andrew - "rages" is a typo for "rags".
*
Ombudsman,
Your half-bay suggestion sounds like it would partly solve what I am guessing would be a problem. That is, dealing with all of the outlet/switch boxes that protrude 1/2" past the studs. How did you get a good seal with these in the bay/way? With your half-bay suggestion, most of the outlets would be within the lower sheetrock; however, the switch boxes would still have to be dealt with. Taking your suggestion one step further, how about installing 8' of sheetrock in a 9' wall? That would eliminate having to deal with any of the boxes. It would also make for a much smaller area to seal. The negatives to this that I can think of are: (1)Sheetrock is usually installed with the first sheet butted up to and supporting the ceiling, (2)You're having to work a staged (partial installation and subsequent return) with the sheetrocker. (3) You can't see that the DP cells really DP everywhere. In your experiences, if you inserted the hose into the bay to a position lets say 3' above the bottom (ie hose blocked by wire) would it sufficiently dense pack that 3'?
Dave L.
*
The half-bay suggestion was spontaneous; there are likely a hundred ways to approach it. If you're doing you own rock, you can be flexible; with a pro, I think I'd ask them to do the whole thing and then cut/patch blow-in holes myself. They're not going to want to come back and will be unhappy putting sheets over the filled bay -- if any cellulose gets on top of the stud, you can't get the sheet on right.
Someone here has said a few times that he routinely leaves a 6" gap at the middle & fills the wall there. After inspection, he closes it up. The smaller the gap you work with the better, because the cellulose will squirt out any openings it finds. In my case, holes in the wood finish & only wall wouldn't work. For the outlet box, I think just stuffed whatever was lying around into the gap -- it really is pretty easy.
Little things in the wall like wire & boxes won't cause voids if the mixture is "lean". Better to start at the bottom and fill from the top down -- if the cellulose stays at the top, the most likely area for a void, you know it's stuck good.
If you need precise advice, this place is home to the cellulose gurus -- Bill and Freddy are particularly clever.
*
Dear Fred,
I talked some more with our local building inspector and with a cellulose manufacturer (Greenstone a Louisiana Pacific Co. They have combined several of their brands under the single Cocoon brand). A couple of things came up that I haven't seen discussed. First, on your site and elsewhere DP is described to be at 3.5 lbs/ft. The Cocoon factory rep was citing wall density at 2.6 lbs/ft. When I asked him about the 3.5 lb figure, he said that depends on the "grind" of the cellulose. The newer grinds are installed at a lower density with the same result. He said 2.6 lbs/ft would be the density with the new grind. Does that sound correct to you? I wonder about the air infiltration characteristics of the newer grind. Your comments?
Also, our local inspector is taking the position that if he can be provided with any "listing" info on a product, then he'll accept it. He says that a product is normally listed with UL, BOCA?, CABO?, etc. If it's shown to be installed a certain way with them, then he's happy. The Cocoon rep read me their installation recommendations which were: no vapor retarder under sheetrock, and no venting in cathedral ceilings(except where required by code). He's checking on the basis of those recommendations and if there is any "listing" info. Do you know of any regulatory agency that cellulose has been "listed" with using the no vapor retarder/no venting recommendations? I can understand the inspector's position. He wants something other than some supposed expert saying this is the way to do it. He needs something official to answer to the subsequent homeowner who complains of a particular building technique.
Looking for ammo,
Dave L.
*Dear Fred,After rereading my last post, I feel it appropriate to clarify a statement I made. In referring to our local inspector, I said "he wants something other than some supposed expert saying this is the way to do it". I did not mean to imply that "I" consider you to be "some supposed expert". I am a "believer", and like many other frequenters of this thread, consider you one of the "foremost" experts, and value your opinion. My intended point was that our inspector says he has heard of lots of techniques supported by "supposed experts" and won't sign off on something based solely on their recommendations.Still looking for ammo!
*
How about a pseudo-Southern climate (No. VA)? I assume venting becomes important for releasing solar heat at some point? (Or does ASHRAE not go as far as New England FREDL?)
*Fred, I may have parsed your initial response too fine ("The current handbool states in Chapter 23 that roof venting in northern climates should be optional and not a code requirement."). Inclusio unis, exclusio alterus. You know, lawyers. Comparative roofology: As long as you're "here" -- we just received our first decent snowfall in No. VA (8", largest in 3 years -- and people are complaining about it? 3 feet in Ithaca, i still had to go to school). Beautiful. Yesterday was warmer but overcast. I did a brief neighborhood tour to see who's roof snow was melting (never thought about it before). Virtually all the houses around here have about the same roof pitch, different elevations, and most are variations on the basic Cape design. Results: In the new soffit/ridge vented houses, rapid snowmelt at ridge vent, followed by slow melting over rafter bays (in one case, however, the rafter lines appeared first) regardless of cardinal orientation. One guy lost his gutter to the icicles. Unheated building roofs (e.g., our garage), negligible melting. Most curious, our entire 60 y.o. roof had essentially no melting (except over the chimney chase -- yes, I'll deal with it). In fact, all of the unvented/gable vented roofs have no dramatic snowmelt. Can you weave these various observations together sensibly? Can someone else explain why Freddy is wrong, in graphic ad hominem terms? I'll just watch from a safe distance... :)(:
*andrew d. I thought we are supposed to avoid ad hominum arguments? GeneL.
*Just testing. You win a point, Gene.
*. . . thought the play was for dogbones
*
In this forum,I have seen ice dams referred to, but I haven't seen an explanation of how they form. I fear the answer is going to be painfully simple and therefore I have disguised my name to avoid embarassement.
Does the "moist" in hot moist air have anything to do with the ice or is it simply carried along with the "hot"?